update formats and lecture notes

content/Math4111/Math4111_L6.md

@@ -145,7 +145,8 @@ Since $b$ is fixed, so this is in 1-1 correspondence with $A$, so it's countable
 
 Let $A$ be the set of all sequences for 0s and 1s. Then $A$ is uncountable.
 
-Proof:
+<details>
+<summary>Proof</summary>
 
 Let $E\subset A$ be a countable subset. We'll show $A\backslash E\neq \phi$ (i.e.$\exists t\in A$ such that $t\notin E$)
 
@@ -155,4 +156,4 @@ Then we define a new sequence $t$ which differs from $S_1$'s first bit and $S_2$
 
 This is called Cantor's diagonal argument.
 
-QED
+</details>